1. Field of the Invention
The invention relates to a magneto-inductive flowmeter having at least one measuring tube for the flow of an electrically conducting medium, having at least one magnetic field generator for generating a preferably alternating magnetic field running at least also perpendicular to the longitudinal axis of the measuring tube, having at least two measuring electrodes—in particular in contact with the medium—and having a functional unit containing at least one evaluation unit.
2. Description of Related Art
Magneto-inductive flowmeters have been known extensively in the prior art for decades. As an example, reference is made here to the citation “Technische Durchflussmessung” by professor Dr.-Ing. K. W. Bonfig, 3rd Edition, Vulkan-Verlag, Essen, pages 123 to 167 and to the citation “Grundlagen Magnetisch-Induktive Durchflussmessung” by Dipl.-Ing. Friedrich Hoffmann, 3rd Edition, 2003, publication of the company KROHNE Messtechnik GmbH & Co. KG.
The basic principle of a magneto-inductive flowmeter for flow measurement of a flowing medium is traced back to Michael Faraday, who already proposed, in 1832, the use of the principle of electromagnetic induction for measuring the flow velocity of an electrically conductive medium.
According to Faraday's law of induction, an electric field strength is formed perpendicular to the direction of flow of the medium and perpendicular to the magnetic field in a flowing, electrically conductive medium interfused by a magnetic field. Faraday's law of induction is thus exploited in magneto-inductive flowmeters in that a magnetic field fluctuating over time during the measurement process is generated by means of a magnetic field generator having at least one magnetic field coil, normally two magnetic field coils, and the magnetic field at least partially interfuses the electrically conductive medium flowing through the measuring tube. Here, the generated magnetic field has at least one component perpendicular to the longitudinal axis of the measuring tube or perpendicular to the direction of flow of the medium.
If it is mentioned above that the magneto-inductive flowmeter being discussed here has at least one magnetic field generator “for generating a magnetic field running perpendicular to the longitudinal axis of the measuring tube”, then it should be mentioned here that the magnetic field preferably runs perpendicular to the longitudinal axis of the measuring tube or perpendicular to the direction of flow of the medium, however, it is sufficient when a component of the magnetic field runs perpendicular to the longitudinal axis of the measuring tube or perpendicular to the direction of flow of the medium.
It is described above, that the magnetic field generator is specified for generating a preferably alternating magnetic field. This expresses that it is not of importance for the teaching of the invention—according to its origin, according to the underlying object and according to the solution of this object—that there is an alternating magnetic field, even if, for the most part, magneto-inductive flowmeters have magnetic field generators that generate an alternating magnetic field.
It is also described above that the magneto-inductive flowmeter being discussed here also has at least two measuring electrodes—in particular contacting the medium. These measuring electrodes are used for tapping a measuring voltage induced in a flowing medium. Preferably, the virtual connection line of the of the two measuring electrodes runs essentially perpendicular to the direction of the magnetic field interfusing the measuring tube perpendicular to the longitudinal axis of the measuring tube. In particular, the measuring electrodes can be provided in such a manner that their virtual connection line actually runs—more or less—perpendicular to the direction of the magnetic field interfusing the measuring tube.
Finally, it is described above that the measuring electrodes are, in particular, such that they come into contact with the medium. Indeed, of course, the electric field strength generated by induction in the flowing, electrically conductive medium can be tapped by direct, i.e., galvanic measuring electrodes in contact with the medium as a measuring voltage. However, there are magneto-inductive flowmeters in which the measuring voltage is not tapped by direct, i.e., non-galvanic, measuring electrodes in contact with the medium, rather the measuring voltage is capacitively determined.
The primary use of magneto-inductive flowmeters of the type being discussed here is naturally the measurement of the flow of a medium through a measuring tube, namely a medium that has at least a low electric conductivity, i.e., flow measurement. However, the use of magneto-inductive flowmeters is not limited only to this use. Magneto-inductive flowmeters, which are also specified and suitable for conductivity measurement, are known, for example, from the translation of the European patent 0 704 682, German Patent DE 692 32 633 C2, as well as from the publication of German applications DE 102 43 748 A1 (which corresponds to U.S. Pat. No. 6,804,613) and 10 208 258 A1.
That magneto-inductive flowmeters can be specified and suitable for conductivity measurement is only mentioned above as an example that the use of magneto-inductive flowmeters is not limited only to use in flow measurement. Nevertheless, however, magneto-inductive flowmeters are used for a very large spectrum of uses in flow measurement and modern functional units in magneto-inductive flowmeters can cover these uses. Admittedly, parameterization is necessary for different uses—in particular because measuring conditions can be very diverse, for example
constant flow or pulsing flow depending on the type of pump,
few disrupted measuring voltages at the measuring electrodes due to a high conductivity of the medium, whose flow is to be measured, and a clean, pure liquid (e.g., in the chemical industry) as medium or a pulpy medium in the measuring tube having a changing pH and changing conductivity (e.g., in the paper industry) or hydraulic transport of sand in a sand-water mixture or cooling water as a medium with a mixture of air bubbles and dissolved deposits (in the production of steel),
measurement over a long period of time (days, weeks or even months) for determining and possibly deducting volume flows, or in a range of seconds for dispensing exact volumes, or in a range of minutes for filling containers or for precisely regulating the flow at a desired value,
very different nominal widths, nominal widths in a range of a few millimeters to a range of several meters,
measurements in a pump station, far away from further industrial systems or measurements close to inductive smelting furnaces with extreme magnetic fields or measurements in galvanic processes with high electrical currents of more than 10 kA over the medium in the measuring tube or measurements in piping systems with corrosion prevention due to a voltage increase in the medium as opposed to ground potential.
This is only an exemplary list of different uses that require different parameterizations in order to be able to obtain sufficiently exact and sufficiently stable measuring values even in a very short time.
Since there are a plurality of different tasks, measuring principles and producers in the field of measuring technology, experts among the users are no longer readily capable of carrying out the necessary different parameterizations without ado. It is not known to the producers when they deliver their measuring devices, where and how they will be used, so that parameterization by the producer cannot easily satisfy all requirements and dispatching special producer lists at the measuring locations only makes economic sense in exceptional cases.